What are some things people should consider regarding storage before virtualizing servers?
The first thing is a word of caution. A lot of people fail to recognize what the consequences are going to be for their storage infrastructure once they set about pursuing all the goals and objectives that have been laid out and articulated so well by evangelists for server virtualization.
People think, "All I need to do to virtualize all my servers is to get the proper server equipment [and then] equip it with the right host bus adapter [HBA] and network interface card [NIC] count, the right kind of processes [and] the right amount of memory, then we just drop that into the existing infrastructure and it will talk to the back-end storage." Unfortunately, it's not like that because you're significantly altering the input/output (I/O) patterns in your storage fabric across your IT network -- or however you have your storage attached currently -- from what they were prior to the workloads established when virtualizing servers.
Server virtualization is essentially like Jenga; you take all your applications, stack all the bricks up and hope that somebody doesn't pull out one of the bricks and everything falls to the ground. But what you're doing in the process is taking multiple servers and consolidating them onto fewer platforms. To accommodate the workload requirements, you usually add additional HBAs and NICs to the server kit to attach sufficient bandwidth to do the work you need to do. At the end of the day, you have fewer boxes, but each box is overprovisioned because each one needs to be a hosting environment for the failover of another box; so, you're basically driving up the cost of server computing -- and people don't realize that -- from what it was when it was a bunch of disparate machines. You're also changing the traffic pattern across whatever interconnects you have going to your storage, so be aware of that. You may want to do it in a piecemeal fashion and test it every step of the way to see where you're going to run into potential logjams with I/O. The No. 1 complaint people have about server virtualization is that their applications slow down.
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